In the past, voids (air bubbles) generated in a hot blast (air) reflow processing in normal atmospheric pressure during a reflow mounting process of large current device such as mounting process of power device and power module have been held in question. A method of allowing generation of any voids to be more reduced has been required.
FIGS. 19A and 19B are processing diagrams for showing the hot blast reflow processing according to a past example. Cream solder 8 shown in FIG. 19A is applied onto a pad electrode 4 of a substrate 5. The cream solder 8 is formed by adding flux to solder powder so as to have an appropriate viscosity. The cream solder 8 is applied onto the pad electrode 4 of the substrate 5 by a screen printer through a mask.
In this past hot blast reflow, the hot blast reflow processing is performed on the cream solder 8 and when the solder melts, voids 2 are generated in an interior thereof. Such a problem that when the molten solder 7 is cooled and solidified, these voids 2 remain in the solder as they are has occurred.
The following will schematically describe the voids generation in such a hot blast reflow processing condition that the cream solder 8 is applied onto the pad electrode 5 of the substrate 5 but the electronic component is not mounted, with reference to FIGS. 19A and 19B. The solder 3 shown in FIG. 19B is formed so that the molten solder 7 is cooled and spherically solidified by its surface tension after the cream solder 8 shown in FIG. 19A has been subjected to the hot blast reflow process. Circular white portions shown in the drawing indicate the voids 2 which unsatisfactorily occur in the molten solder 7 and remain in the solder 3 after the cooling and solidification thereof. The voids 2 damage heat conduction effects in the power device and the like and cause waste heat to deteriorate.
Regarding the above-mentioned reduction of the voids occurrence, a patent document 1 discloses a soldering apparatus (vacuum reflow apparatus) having a vacuum evacuation function. This solder apparatus is provided with an exhaust valve, a vacuum pump and a treatment chamber. Under the condition in which the substrate is imported into the treatment chamber and the solder on the pad electrode of the substrate is melted, the exhaust valve is opened and the vacuum pump is driven so that the interior of the treatment chamber can be once evacuated. Such a vacuum condition allows any voids which remain in the solder while the solder is melted to be removed by defoaming and/or deaerating effect.